1. Field of the Invention
The present invention relates generally to aerogel composite materials. More specifically, the present invention relates to densified aerogels and densified aerogel composite materials and methods of preparing the same.
2. Description of the State of Art
Low-density materials have been developed to solve a number of thermal isolation problems where the insulation core material experiences high pressures. For instance, polymeric materials have been compounded with hollow glass microspheres to create syntactic foams, which are typically very stiff, compression resistant materials. Syntactic materials are well known as insulators for underwater oil and gas pipelines and support equipment. However, syntactic materials are relatively inflexible and exhibit high thermal conductivity relative to flexible aerogel composites (aerogel matrices reinforced by fibers.)
Aerogels describe a class of material based upon their structure, namely low density, open cell structures, large surface areas (often 900 m2/g or higher) and sub-micron scale pore sizes. Supercritical and subcritical fluid extraction technologies are commonly used to extract the solvent from the fragile cells of the material. A variety of different aerogel compositions, both organic and inorganic are known in the art. Inorganic aerogels are generally based on metal alkoxides and include materials such as silica, zirconia, titania, alumina, carbides and many others. Organic aerogels can include carbon aerogels and polymeric aerogels such as polyimides aerogels.
Low density aerogels (0.02-0.2 g/cc) based on silica are excellent insulators, better than the best rigid foams with thermal conductivities of 10 mW/m-K and below at 100° F. and atmospheric pressure. Aerogels function as thermal insulators primarily by minimizing conduction (low density, tortuous path for heat transfer through the nanostructures), convection (very small pore sizes minimize convection), and radiation (IR suppressing dopants may easily be dispersed throughout the aerogel matrix). Depending on the formulation, they can function well at temperatures of 550° C. and above. However, in a monolithic state they tend to be fragile and brittle and are thus not well suited for most applications outside of the laboratory. The aerogel materials presented herein, address such requirements.